1. Field of the Invention
The present invention relates to a light detection device which is used for an optical disk system, a laser printer, etc.
2. Description of the Related Art
In conventional optical disk system, a light beam irradiated from a semiconductor laser was led to a prism in a light transmission system. The light beam reflected by this prism was led to a photo-detector. The output of semiconductor laser was detected by the photo-detector, and the output light quantity of the semiconductor laser was controlled by this detected quantity. In this case, in order to increase the light reception efficiency of the photo-detector, a convergent lens was provided in front of the photo-detector.
However, when a convergent lens is provided in front of the photo-detector in this way, reflected light from the light receiving face of the photo-detector is led to the reproduction system of the optical disk system via the prism in the light transmission system. Thus, deterioration of the reproduction signal sometimes occurs.